Photosensitized xanthone-based oxidation of guanine and its repair: A laser flash photolysis study

The photosensitized oxidation of guanine (G) by the triplet state of xanthone (XT) and the repair for photo-damaged G(–H) by ferulic acid (FCA) were investigated using the laser flash photolysis technique. The rate constants of the reaction of triplet state of XT with G and with FCA were determined as 4.5 × 109 and 8.0 × 109 L mol−1 s−1, respectively. Laser exposure was performed on the N2-saturated acetonitrile/water (v/v, 1:1) solution containing G, XT and FCA. The transient absorption spectra indicated that the triplet state of XT first reacted with G predominantly to form the oxidized radical G(–H). The radical G(–H) was rapidly repaired by FCA, and the rate constant for the repair reaction was determined as 1.1 × 109 L mol−1 s−1. These results demonstrated that non-enzymatic repair is a feasible method for repairing photosensitized DNA bases oxidation.